Cardiolipin (hereinafter sometimes referred to as CL) is a kind of phospholipid, and is widely distributed in animals, plants, and bacteria. Cardiolipin accounts for 1 to 15% of total phospholipids in animals and plants, and 50% of total phospholipids in some bacteria. Cardiolipin has the following structure,
wherein R1, R2, R3, and R4 each represent a chain hydrocarbon group.
CL is a phospholipid mainly present in mitochondria in mammalian cells. CL therefore controls various enzyme activities present in mitochondria that include an electron transfer system, and takes part in apoptosis. In particular, a large amount of CL is contained in a cardiac muscle cell.
Conventionally, CL is quantified using a thin-layer chromatography and a phosphorus quantification method. However, these methods exhibit low detection sensitivity and low quantification accuracy, and require time and effort. Mass spectrometry for CL has not been established.
Thus, although CL is an important and essential component in the body, analysis methods thereof are extremely scarce even today.
The present inventors have developed enzymatic fluorometric measurements for phospholipids (phosphatidylcholine, phosphatidylethanolamine, phosphatidic acid, phosphatidylserine, and sphingomyelin) (Patent Literature 1 and 2).
Patent Literature 1 reports an enzymatic quantification method of phosphatidylserine in which the fluorescence intensity of a compound produced by treating a sample with phospholipase D, L-amino-acid oxidase and peroxidase is measured.
Patent Literature 2 reports an enzymatic quantification method of sphingomyelin in which the fluorescence intensity of a compound produced by treating a sample with sphingomyelinase, alkaline phosphatase, choline oxidase, and peroxidase is measured.
However, since an enzymatic quantification method of CL has not been developed, an inability to determine the profile of all phospholipid classes by excluding CL is a problem.